Piston



A. L. NELSON I June 8, 1937.

PISTON 2 Sheets-Sheet 1 Original Filed Deg. 7, 1927 June 8, 1937. A. L. NELSON 2,082,898

PISTON Original Filed Dec. 7, 1927 2 Sheets-Sheet 2 Patented June 8, 1937 UNITED STATES PISTON Adolph L. Nelson, Detroit, Mich, assignor to Bohn Aluminum & Brass Corporation, Detroit,

Mich.

Application December 7, 1927, Serial No. 238,249 Renewed March 26, 1931 4 Claims. (01. 309-43) This invention relates to pistons, and particularly to pistons adapted for use in internal combustion engines.

The invention applies especially to a piston constructed of light but relatively highly expansible material in which the expansion of the upper part of the skirt is controlled by struts of relatively less expansible material. A particular object is the formation of the lower part of the skirt in an unbroken ring free from vertical slots. This construction facilitates machining and combines with the controlling struts to produce a desirable expansive action of the entire cylinder-bearing portion of the piston skirt.

A further object is the provision of a frame strut having an opening to accommodate the piston pin, the ends of the strut carrying spadehandle grips anchored in the material of the piston skirt. Means are provided to adapt the strut for use with a set screw holding the piston pin in position.

An additional feature is the use of inclined slots separating. the upper ends of the cylinderbearing portions from the skirt, thereby providing for the maximum length of the cylinder bearing portions for a given over-all length of the piston.

While preferred embodiments of the invention have been disclosed for purposes of illustration, it should be understood that various changes may be made in the structurewithout departing from the spirit and scope of the invention as hereinafter set forth and claimed.

In the drawings:

Fig. 1 is an elevation of an automobile piston.

Fig. 2 is an elevation partlyin section taken at right angles to Fig. 1.

Fig. 3 is an elevation of the strut used in Fig. 1.

Fig. 4 is an elevation of a modified form of 40 strut.

Fig. 5 is a vertical section through a piston embodying thestrut of Fig. 4.

Fig. 6 is a bottom plan of the piston of Fig. 5, parts being removed. Fig. 7 is a view similar to Fig. 5 showing a further modification.

Fig. 8 is a bottom of the piston of Fig. 7.

Fig. 9 is an elevation of'the strut used in Fig. 7, the strut being shown before bending.

Fig. 10 is a view similar to Fig. 9 but showin the strut after bending.

Referring to the drawings more particularly, the reference character l0 indicates the head of the piston, while numerals II indicatepiers depending from the head and having piston pin bosses I2 formed therein. The lower end of the piston skirt forms an annular portion I; which is connected to the lower ends of the piers ll. Tongues l4 extend upwardly from the annular portion l3, these tongues being located between the piers and being spaced from the piston head by slots l5 and from the piers by vertical openings iii.

The parts thus far mentioned are preferably formedv of some suitable light-weightmaterial such as aluminum alloy, and in order to control the diametrical expansion of the upper ends of the tongues M, a pair of struts ll of some material less expansible than the piston material are placed across the piston with their ends enthe top frame and extending into the ear IS.

The vertical ends of the frame carry spadehandie grips 20, provision being made for either a single grip at the upper part of each end, as shown in Fig. 3, or for a plurality of grips on each end as shown in Fig. 9. These spade grips are bent to the rear as seen in Fig. 3 so that they conform to the curvature of the piston. The lower frame member carries projections 2| extending upwardly near its middle portion.

In forming the piston the struts l! are first accurately positioned in the mold and are held securely in position while the metal forming the piston is cast about them. In this manner the upper and lower members of the strut are embedded in the piers above and below the piston piri bosses, and the spade-handle grips are embedded in the cylinder-bearing surfaces It.

In the piston as it leaves the casting mold the cylinder-bearing portions are integral with the material of the piston head, and these parts are later severed by cutting the slots l5. The piston head is formed with ring grooves 22, and in cutting the slots [5 it is desirable to leave below the lower groove 9. land 23 of suflicient strength. while at the same time giving the cylinder-bearing portions the greatest length possible. This is accomplished by cutting the slots l5 at an inward and downward angle to meet the upper ends of the openings IS, a result attained by tilting to the required angle the rotary cutter disc used in the slotting operation.

With the construction described the relatively inexpansible struts exert a positive controlling influence on the diametrical expansion of the upper ends of the cylinder-bearing portions, so that it is possible to fit this end of the skirt with a close clearance in the cylinder. But it is necessary to make some provision to prevent the lower end of the skirt from binding under the expansive action of operating temperatures, and the present invention contemplates doing so without the use of longitudinal slots extending upward from the lower edge of the skirt. The invention also improves the bearing conditions at l6.

In carrying out this purpose slots 24 extending from the lower ends of openings iii are formed in the skirt. These slots may run at any desired angle, the important consideration being that they must not extend to the lower edge of the skirt. The slots 28 may be cast into the skirt as in Fig. '7 or they may be cut after casting as in Fig. 1. The efiect of these slots is to free the cylinder-bearing portions it from being bent inwardly on diameter CDfrom the efiect of the expansion of the skirt on the diameter AB parallel to the axis of the piston pin. The increase in diameter AB is shown on a somewhat exaggerated scale in Fig. 6 in which the dotted lines show how the skirt tends to expand on the diameter A B without forcing the skirt inwardly on diameter CD. Without the slots 26 the skirt is bent inwardly on diameter CD due to the fact that the skirt from the point A to point C acts as a lever fulcrumed about the end of the strut, and hence outward movement at A causes inward movement at C. The result has a tendency to make the piston slap when engine and oil are hot, because the cylinder expansion is greater than the resultant expansion of the piston on diameter CD. This action is mostly at the lower end of the skirt, but it also extends to the top of the skirt on the diameter perpendicular to the piston pin.

It is desirable to have the diameter CD expand slightly faster than the cylinder in order to reduce the clearance and compensate for the thinning of the oil as the motor warms up. The length of the slots 24 controls the relative expansion on diameter CD, the longer the slots 24 the greater the expansion at CD.

The control of the skirt expansion afiorded by the slots 24 permits the cylinder bearing portions of the skirt to take a better bearing in the cylinder along the vertical center line of the bearing portions. This helps to distribute the wear even- 1y over the surface of the cylinder-bearing portions and gives a uniform bearing for the entire skirt portion in contact with the cylinder.

In connection with the slots 24 it is necessary to form the skirt in such a manner that the portions of rings l3 lying on diameter AB cannot expand into harmful contact with the cylinder walls. One method of doing this is to relieve the surface of ring l3 below the pin bosses bygrinding down these parts of the ring as indicated at 25 in Fig. 1. A similar result may be obtained by giving the lower end of the skirt an oval shape with the short axis on diameter AB, or the skirt may be tapered so that the lower end of the skirt has a greater initial clearance in the cylinder than the upper end.

In some cases it may be advisable to provide a set screw 26 (Fig. 5) to secure the piston pin in position, and the strut should then be arranged to permit passage of the screw through the pin boss. This may be done by interrupting the lower member of the strut as at 21 in Figs. 4 and 5, or by forming the lower member with an arched bridge clearing the screw as in Figs. 7-10. In this latter embodiment the strut is stamped out in the shape of Fig. 9 with the arched portion 28, and in the forming operation the bridge is bent to the rear as indicated in Fig. 10 so that in the resulting piston the bridge 28 extends around the screw in the manner illustrated in Fig. 8.

The piston may be provided with two arcuate ribs 29 which strengthen the ring l3 below the pin bosses, and these ribs may be near the lower edge of the skirt as in Fig. 2 or they may be spaced upwardly from the lower edge as in Fig. '7.

I claim:

1. A piston comprising a head, piers depending from the head, cylinder-bearing portions connected to the piers and formed of relatively light-weight material, and struts of relatively inexpansible material connecting the cylinderbearing portions, the upper ends of the cylinderbearing portions being separated from the head by straight, inclined slots.

2. A piston comprising a head, piers depending from the head, cylinder-bearing portions connected to the piers and formed of relatively light-weight material, and struts of relatively inexpansible material connecting the cylinderbearing portions, the upper ends of the cylinderbearing portions being separated from the head by straight slots inclined downwardly toward the center of the piston so that the central part of each cylinder-bearing portion extends farther toward the piston head than do the lateral parts of the cylinder-bearing portion.

3. A piston comprising a head, piers depending from the head and having piston pin bosses formed therein, cylinder-bearing portions lying between the piers and formed of relatively lightweight material, and a pair of frame struts of relatively inexpansible material extending between the cylinder-bearing portions and surrounding the pin bosses, each strut having a lower member, the lower member of a strut being formed with an opening to permit passage of a set screw upwardly into a boss.

4. A piston comprising a head, piers depending from the head and having piston pin bosses formed therein, a set screw extending upwardly into a pin boss, cylinder-bearing portions lying between the piers and formed of relatively lightweight material, and a pair of frame struts of relatively inexpansible material extending between the cylinder-bearing portions and surrounding the pin bosses each strut having a lower member, the lower member of a strut being deformed to extend around the set screw.

ADOLPH L. NELSON. 

